Substance P (SP) is a neurotransmitter for neuromuscular junction and pain regulation as well as a modulator for the dopaminergic system. Studies were conducted to determine the distribution of SP in the granula of different densities from bovine adrenal medulla. The biosynthesis of SP was studied in tissue cultures of hypothalamus, substansia nigra and caudate. Studies were also conducted to investigate the effect of hypophysectomy, adrenalectomy, and splanchnic nerve denervation, on blood pressure and distribution of SP in the central nervous system (CNS) and peripheral system in normal and hypertensive rats. Specific antibodies against SP raised rabbits have been isolated and purified for the purpose of obtaining an idiotipic antibody for the purpose of identifying the SP receptors.